The present invention is directed to the controller of an air conditioning system, and more particularly, to method and apparatus for using a single electrical control line to determine whether a load is present on that line, and then controlling that load using the same line. For purposes of the present invention, a load can mean both a directly controlled device such as a light, an actuator, or a solenoid, or an indirectly controlled device such as a compressor motor actuated by such load controlling circuitry as a relay.
Controllers for refrigeration systems and the like are limited by physical constraints and economics to a finite number of input and output lines. Often the number of available lines is insufficient, especially if certain lines are dedicated to seldom used functions such as system configuration. In system configuration, lines provide a plurality of binary inputs, such as configuration jumpers, DIP switches or the like, to a system controller indicating the connection or non-connection of a particular system load. Multiplexed lines and bus structures are often resorted to in order to obtain more input/output lines. This can be very costly and very complex in terms of system time, data management, and component costs.